Hi Javier,
To achieve a good non cut out animation you first need a good key frame drawings. First draw (with paper and pencil or whatever other media) your key poses. If you can show the key poses with the right timing to tell a story then you have 50% of the work done.
Once you finished the animatics then import it to Synfig using the list importer layer or simply animating the file name of a image layer. Then trace over a key frame and tween to the rest.
See this post for an example:
God luck!
-G